As is widely known, automobile manufacturers desire the flexibility to offer a variety of drivetrain packages with different power transmission characteristics (i.e., number of gear ratios, torque capacity, 2WD/4WD, etc.) for each vehicle. This flexibility is limited, however, by the significant cost and leadtime required to design and validate a series of different power transfer devices (i.e., transfer cases, transmissions, transaxles, axle assemblies, etc.). This dilemma is further aggravated by the competitive need to develop lighter weight and higher efficiency power transfer devices at a reduced cost.
A significant amount of the weight and manufacturing cost associated with traditional power transfer devices is derived from the housing. Typically, the housing is assembled from two or more bell-shaped castings that are interconnected to form an enclosed chamber within which a geartrain is supported. Additionally, the various rotary components (i.e., shafts, gears, carriers, etc.) of the geartrain extend through and/or are rotatably supported by one or more of the castings. As such, each casting must be constructed from a material having sufficient strength and thickness to absorb the loads created during power transmission while providing acceptable noise isolation and heat transfer characteristics. Consequently, most housings are designed for use with a single power transfer device. Hence, increased costs are incurred when a variety of drivetrain packages are offered to the consumer.
Another disadvantage associated with conventional housings is the secondary machining required to permit the castings and the drive components of the geartrain to be properly aligned during assembly. For example, since threaded fasteners are used to rigidly connect the castings, the flatness of the mounting face on the rim of each casting and the location of threaded holes therein are critical to proper alignment and sealing of the power transfer device.